feat: 重构为 Monorepo 架构并实现 HTTP Server

架构变更:
- 采用 pnpm workspaces 实现 Monorepo 结构
- 将现有代码迁移到 packages/core
- 新增 packages/server HTTP 服务层

Server 功能:
- REST API: 会话管理、工具管理、配置管理
- WebSocket: 实时双向通信支持
- SSE: 服务端事件推送
- Hono + Bun 作为运行时

API 端点:
- GET/POST /api/sessions - 会话 CRUD
- GET/POST /api/sessions/:id/messages - 消息管理
- GET /api/sessions/:id/events - SSE 事件流
- WS /api/ws/:sessionId - WebSocket 连接
- GET/POST /api/tools - 工具管理
- GET/PUT /api/config - 配置管理

packages/core/src/tools/descriptions/undo.txt

@@ -0,0 +1,14 @@
+Undo the most recent file operation by restoring to the previous checkpoint.
+
+This is a quick way to revert the last change. It restores all files to their state at the second-most-recent checkpoint (since the most recent checkpoint captures the current state).
+
+Parameters:
+- confirm: Set to false to preview what would be undone without executing (default: true)
+
+Usage:
+- Quick undo: undo
+- Preview first: undo confirm=false
+
+If you need to undo multiple operations or restore to a specific point, use checkpoint_list and checkpoint_restore instead.
+
+After undo, you can "redo" by using checkpoint_restore with the previous commit hash (shown in the output).